Characterization and etching of sputter-deposited absorber films for extreme ultraviolet lithography (EUVL) masks

Abstract

Fabrication of masks for EUVL requires the formation and patterning of both repair buffer and EUV absorber layers on top of a molybdenum/silicon multi-layer substrate. Films used for buffer and absorber should have low stress, good uniformity and good etch selectivity to underlying layers. Low stress chromium and tantalum nitride absorber film deposition processes have been developed and characterized on fused silica substrates at the MCoC. Sputtered silicon oxide was used as the buffer layer for work reported in this paper. This paper describes the results of EUVL mask processing at the MCoC, including deposition and etch capabilities of these films. Properties of the low stress chromium and tantalum nitride materials will be discussed, including stoichiometry, stress, uniformity and density. The chromium and tantalum nitride films have been integrated into a mask patterning process with a silicon oxide buffer layer. Etch bias and etch profiles from the two absorber films along with etch selectivities to the underlying silicon oxide layer will be presented. Image size results for both types of absorber layers will be presented, including the improvement in etch bias using the low stress chromium Complete EUVL masks with 160 nm feature sizes have been fabricated with these processes and micrographs of nested lines and elbows will be presented.